TUBULAR KING PILE FOUNDATION SYSTEM- Robust and Resilient Foundation System with High Cost Efficiency -Vol.1 Design

Table of Contents
Chapter 1

Introduction ············································································································1

Chapter 2Foundation Configuration ·······················································································1

Chapter 3

Foundation Properties ····························································································2
3-1 Denomination of the Tubular King Pile Foundation ·············································2
3-2 Properties of Tubular King Pile Foundation ·························································3

Chapter 4Foundation Wall Design ··························································································34-1 General ·············································································································34-2 Embedded Depth of Tubular King Pile Foundation ··············································4
4-3 Passive Mobilisation Mechanism ······································································6
4-4 Durability ··········································································································8

Chapter 5

Design Case Study ···································································································95-1 Introduction ······································································································95-2 List of Design Standards and References ·························································10
5-3 Ground Conditions ··························································································11
5-4 Design Approach ·····························································································13
5-5 Design Assumptions ························································································15
5-6 Assumed Construction Sequence ····································································18
5-7 Results ············································································································19
5-8 Summary ········································································································23

Chapter 1

Introduction

The purpose of this document is to provide model practice guidelines for the design of the Tubular
King Pile Foundation to be installed, using the Press-in Piling Method.
The press-in piling method is commonly used worldwide because of its very quiet operation, ultra
low vibration, and flexibility of sizes to suit different wall properties and subsoil conditions.
The main attributes of the Tubular King Pile Foundation are efficiency of physical properties andversatility. The Tubular King Pile Foundation comprises steel tubular piles as the primary
foundation elements and incorporating additional upper wall elements on top of the steel tubularpiles. The efficiencies of physical foundation properties can be optimised in view of the flexibility ofpile size and the spacing of tubular piles for the ground conditions and the form of the loading.

Chapter 2Foundation Configuration

Tubular King Pile Foundation is a combined foundation with great bending stiffness, which
incorporates the following elements.
1. Steel Tubular Piles: Primary elements (High modulus main structural elements)
Tubular piles resist lateral load when used as a retaining wall or barrier, and vertical loads
when used as bearing piles.
2. Upper Wall: Wall elements (Soil-retaining and load-transferring elements)
The Upper wall transfers soil pressure, vertical loads and horizontal dynamic loads to thetubular piles.

Figure 1. Foundation Configuration

1

Chapter 3Foundation Properties

The steel tubular piles of the Tubular King Pile Foundation are installed to a depth necessary toachieve the required passive toe resistance while the upper wall can be incorporated only above
the steel tubular piles to act as a barrier for the soil or dynamic loads.
The steel tubular piles and upper wall are integrated with reinforcement bars or shear connectors
to achieve effective load transfer.

3-1

Denomination of the Tubular King Pile Foundation

The profiles of the Tubular King Pile Foundation are related to their dimension as follows:D1000 -OutsideDiameter ofTubular Piles

18 @ 2500

Thickness ofTubular Piles

2

Pile Spacings
(mm)

3-2

Properties of Tubular King Pile Foundation
OutsideDiameter(mm)

Wallthickness(mm)

InsideDiameter(mm)

Spacing(mm)

SectionModulus
Z (cm3)

SectionModulusZ(cm3/m)Allowable
Stress(N/mm2)

Moment ofInertia I(cm4)

Moment ofInertia I(cm4/m)Elastic
ModulusE X 108(kN/m2)

E I(kNm2/m)MomentCapacity(kNm/m)Massper mof pile(kg/m)

Mass
per m2of wall(kg/m2)

D800 - 12 @ 2000

800

12

776

2,000

5,766

2,883

231

230,632

115,316

2.05

236,398

665

233

117

D800 - 14 @ 2000

800

14

772

2,000

6,676

3,338

231

267,050

133,525

2.05

273,727

770

271

136

D800 - 16 @ 2000

800

16

768

2,000

7,573

3,786

231

302,907

151,453

2.05

310,479

874

309

155

D800 - 18 @ 2000

800

18

764

2,000

8,455

4,228

231

338,207

169,104

2.05

346,662

976

347

174

D1000 - 12 @ 2500

1,000

12

976

2,500

9,091

3,636

231

454,544

181,818

2.05

372,726

839

292

117

D1000 - 14 @ 2500

1,000

14

972

2,500

10,542

4,217

231

527,116

210,8462.05

432,235

973

340

136

D1000 - 16 @ 2500

1,000

16

968

2,500

11,976

4,790

231

598,797

239,5192.05

491,014

1,105

388

155

D1000 - 18 @ 2500

1,000

18

964

2,500

13,392

5,357

231

669,596

267,8382.05

549,069

1,236

436

174

D1000 - 20 @ 2500

1,000

20

960

2,500

14,7905,916

231

739,518

295,807

2.05

606,405

1,365

483

193

D1000 - 22 @ 2500

1,000

22

956

2,500

16,1716,469

231

808,572

323,429

2.05

663,029

1,493

531

212

D1200 - 14 @ 2800

1,200

14

1,172

2,800

15,2885,460

231

917,281

337,600

2.05

692,080

1,261

409

146

D1200 - 16 @ 2800

1,200

16

1,168

2,800

17,3856,209

231

1,043,072

372,526

2.05

763,678

1,434

467

166

D1200 - 18 @ 2800

1,200

18

1,164

2,800

19,4606,950

231

1,167,577

416,992

2.05

854,833

1,605

525

187

D1200 - 20 @ 2800

1,200

20

1,160

2,800

21,5137,683

231

1,290,805

461,002

2.05

945,054

1,774

582

207

D1200 - 22 @ 2800

1,200

22

1,156

2,800

23,546

8,409

231

1,412,765

504,559

2.05

1,034,345

1,942

639

228

D1200 - 25 @ 2800

1,200

25

1,150

2,800

26,556

9,484

231

1,593,346

569,052

2.05

1,166,556

2,190

724

258

Tubular King Pile Foundation

Table 1. Foundation Profiles

Chapter 44-1Foundation Wall Design

GeneralTubular piles, as the primary elements of the Tubular King Pile Foundation system, act as theretaining elements against the earth and water pressures transferred via the secondary element,
i.e. RC upper wall. Thus, the design of the wall system can be undertaken as a continuous retainingwall.
One of the advantages of this system is that, dissimilar to conventional steel sheet piled walls, thedifferential pore water pressure between the active and the passive sides can be considerednegligible below the underside of the RC upper wall since there are sufficient gaps between the
tubular piles for the groundwater to be equalised between the sides.

3

4-2

Embedded Depth of Tubular King Pile Foundation

Figure 2. Cross Section (Retaining Wall)

Figure 3. Cross Section (Barrier)44-2-1

Embedded Depth of Tubular Piles D pri

Limit equilibrium methods can be used to assess the required embedded depth of tubular piles.
The methods use an approach based on soil and groundwater parameters that tend towards worst
credible values and assume that the full strength of the ground is mobilised uniformly around thewall so that the wall is at the point of collapse.
Design parameters could govern the embedded depth of the tubular piles are:










stratigraphy;
soil unit weight;
soil strength (cu, c', φ');groundwater levels;
surcharge loads;
horizontal impact loads;
retained height;
durability/corrosion rates; andpropped or cantilevered.

4-2-2

Embedded Depth of RC Upper Wall Duw

The RC upper wall is only required from the retained surface to the formation level. In practice thebase of the upper wall is extended below the formation level to take into account unplanned
excavation. Besides, careful consideration should be given to drainage design of the RC upper wall
to minimise the occurrence of high differential water pressure.

5

4-3

Passive Mobilisation Mechanism

When the tubular piles are loaded laterally, distribution of the soil stresses can be simulated basedon the Theory of Elasticity using the Boussinesq equation that considers a point load on thesurface of a semi-infinite, homogeneous, isotropic, weightless, elastic half-space. The concept of
the pressure bulb prepared from the Boussinesq's equation by Bowles [1996], as shown in Figure 4,
is useful to visualise the pressure developed in the effective passive area.

Figure 4. Pressure bulbs formed on the passive side of a tubular pile, showing the intensityof pressure q/q0,based on the Boussinesq equation (after Bowles [1996])

The lateral force transferred from the upper wall, resulting from the earth/water pressures andsurcharge load and etc., are resisted by the passive pressure developed in the effective passivezone as schematically presented in Figure 5.
Though there is no simple relationship between the characteristics of the effective passive area(nD) and soil conditions as any relationship is dependent on the tubular pile size/spacing and on
the nature and sequence of the strata, "nD" at a certain distance (H) in low strength cohesive soil isgenerally greater than that in dense cohesion less soil.
_____________________________
1

Bowles, J.E. [1996] Foundation analysis and design - 5th edition, McGraw-Hill, Singapore.
6

Figure 5. Schematic effective area for passive soil pressure

7

4-4

Durability

The effective life of the Tubular King Pile Foundation depends upon the combined effects ofimposed stresses and corrosion.
Performance is clearly optimised where low corrosion rates exist at positions of high imposed
stresses.
Eurocode 3: part 5 considers the end of the effective life of steel piles to occur when any part ofthe pile reaches the maximum permissible working stress as a result of loss of section due tocorrosion.
The tubular piles may be exposed to different combinations of environments. The following tableindicates the mean loss of thickness due to corrosion for these environments in temperate
climates over a given life span.
4-4-1

Loss of thickness (mm) per face due to corrosion of steel tubular piles in soils,
with or without groundwater
Environments

5 years

25years

50years

75years

100years

125years

Undisturbed natural soils(sand, silt, clay, schist…)

0.00

0.30

0.60

0.90

1.20

1.50

Polluted natural soils andindustrial sites

0.15

0.75

1.50

2.25

3.00

3.75

Aggressive natural soils(swamp, marsh, peat…)

0.20

1.00

1.75

2.50

3.25

4.00

0.18

0.70

1.20

1.70

2.20

2.70

0.50

2.00

3.25

4.50

5.75

7.00

Non-compacted andnon-aggressive fills(clay, schist, sand, silt…)
Non-compacted andaggressive fills (ashes, slag…)

Table 2. Corrosion Rates in Soil, with or without groundwater

Note1; Corrosion rates in compacted fills are lower than those in non-compacted ones. In
compacted fills the figures in the table should be divided by two.
Note2; The values given for 5 years and 25 years are based on measurements, whereas the othervalues are extrapolated.

8

Chapter 5
5-1

Design Case Study

Introduction

These calculations detail a design case study of the Tubular King Pile Foundation system forming a
7m-high permanent retaining structure for widening of motorway that has been constructed on an
embankment fill. The retaining structure comprises steel tubular piles of 1000mm external
diameter (with the wall thickness of 14mm) at 2.5m centres and a continuous reinforced concretewall. The design life of the structure has been considered to be one hundred years.
The Geosolve WALLAP software has been used to analyse the retaining wall in accordance with BS
EN 1997-1, based on factoring of surcharge loadings, soil strength parameters and an additional
overdig allowance. The code is based on the use of limit equilibrium methods and uses anapproach based on soil and groundwater parameters that tend towards worst credible values todevelop an adequate margin of safety. The wall’s cross section has also been verified against
structural failure, using unfactored soil strength, factored surcharge loadings and an additional
overdig allowance. These ultimate limit state analyses were followed by a serviceability limit state
analysis, using unfactored soil strength and action, to determine the predicted wall deflection,
based on WALLAP.
In order to estimate ground movements adjacent to the retaining walls soil/structure interaction
analyses have also been carried out using a two-dimensional (2D) finite element (FE) software
package "Plaxis".
Results of the design and associated findings will be presented in this section.

9

5-2
















List of Design Standards and References
Bond, A. and Harris, A. [2008] Decoding Eurocode 7, Taylor and Francis, London.
Borin, D. [2007] WALLAP User's Guide, Ver. 5, Geosolve.
British Standards Institution [1998] Highway parapets for bridges and other structures Specification for vehicle containment parapets of metal construction, BS 6779-1.
British Standards Institution [1999] Execution of special geotechnical work – Sheet pilewalls, BS EN 12063.
British Standards Institution [2004] Eurocode 2: Design of concrete structures, Part 1-1:
General rules and rules for buildings, BS EN 1992-1-1.
British Standards Institution [2004] Eurocode 7: Geotechnical design, Part 1: General rules,
BS EN 1997-1.
British Standards Institution [2005] Eurocode 3: Design of steel structures, Part 1-1: Generalrules and rules for buildings, BS EN 1993-1-1.
British Standards Institution [2007] Eurocode 3: Design of steel structures, Part 5: Piling, BS
EN 1993-5.
British Standards Institution [2010] Road restraint systems - Part 2: Performance classes
impact test acceptance criteria and test methods for safety barriers including vehicle
parapets, BS EN 1317-2.
CIRIA C580 [2003]: Embedded retaining walls - guidance for economic design.
Design Manual For Roads And Bridges [2001] Loads for highway bridges, BD 37/01, Vol. 1,
Section 3, Part 14.
Design Manual For Roads And Bridges [2006] Requirement for road restraint systems, TD
19/06, Vol. 2, Section 2, Part 8.
Plaxis b.v. [2015] Plaxis 2D 2015 - Reference Manual.
Plaxis b.v. [2015] Plaxis 2D 2015 - Material Model Manual.

10

5-3

Ground Conditions

5-3-1

Ground Model

Ground model adopted for the case study has the following geological formations:a) Embankment Fill / Backfill
The Embankment Fill / Backfill comprises compacted granular materials, e.g. sand, gravel,crushed rock and crushed concrete. The material has been assumed as a dense granularsoil.
b) Medium Dense Sand
The material is a layer of naturally deposited sand with relatively uniform medium dense
consistency.
c) Stiff ClayThe material is a heavily overconsolidated stiff clay with a K0 value of 1.5 and thethickness of the formation has been considered to be >20m.
The following stratigraphy has been established for the retaining wall analysis.
Embankment Fill

+7.0m AOD to 0.0m AOD

Medium Dense Sand

0.0m AOD to -5.0m AOD

Stiff Clay:-5.0m AOD11

to -25.0m AOD

5-3-2

Geotechnical Design Parameters

Elevation

Thickness (m)Unit weight (kN/m³)

Angle of Shearing
resistance, φ’peak (Deg.)

Effective cohesion, c'(kN/m²)

Undrained shear strength,cu (kN/m²)

Drained Stiffness, E’(MN/m²)

Undrained Stiffness, Eu(MN/m²)

Drained Poisson’s ratio, ν

Undrained Poisson’s ratio,vu

K0

Coefficient of
permeability, K (m/s)

Embankment
Fill

7.0

7.0

19

38

0

-

10 +
5z

-

0.30

-

0.38

10

-5

8

MediumDense Sand

0.0

5.0

19

35

0

-

25 +
5z

-

0.30

-

0.43

10-5

5

Stiff Clay

-5.0

>20.0

20

20

10

100
+ 7z

80 +
5.6z

100
+ 7z

0.20

0.49

1.50

10-10

12.5

(top of stratum mAOD)

StrataDilatancy angle for drained
analysis, ψ(Deg.)

A summary of the geotechnical parameters used for the retaining wall analysis is presented inTable 3.

Table 3. Summary of geotechnical parameters for the retaining wall analysis

Notes on design geotechnical parameters
1) z is the depth below top of each stratum.

5-3-3

Design Groundwater Levels

The groundwater table has been assumed at -0.5m AOD for the design life of the structure. Due tothe presence of large gaps between the tubular piles, the differential water pressure between theactive and the passive sides can be considered negligible below the underside of the RC upperwall.
It has been assumed that the highway surface water is drained to a sealed carrier pipe via kerbs
and gullies. Besides, owing to the granular nature of the embankment fill materials, thegroundwater level at the back of the RC upper wall is unlikely to build up. Hence, as summarised inTable 4, the design water levels on the active side have been assigned to 0.5m and 0.0m AOD for
the worst credible and moderately conservative cases, respectively.
Design case

Active side [mAOD]

Passive side [mAOD]

Worst credible (ULS)

0.5

-0.5

Moderately conservative (SLS)

0.0

-0.5

Table 4. Design groundwater levels for the retaining wall analysis

12

5-4

Design Approach

5-4-1

Retaining Wall Analysis

The Geosolve WALLAP software (Version 6.05) has been used to analyse the retaining walls inaccordance with Design Approach 1 in BS EN 1997-1 which requires the following analyses:A serviceability limit state (SLS) analysis using unfactored soil strength and action.
An ultimate limit state (ULS) Combination 1 analysis using unfactored soil strength, factored
surcharge loadings and an additional overdig allowance.
An ultimate limit state (ULS) Combination 2 analysis using factored surcharge loadings,
factored soil properties and an additional overdig allowance.

In order to estimate ground movements adjacent to the retaining walls soil/structure interaction
analyses have also been carried out using the 2D FE software package, Plaxis 2D (ver. 2015.1). The
behaviour of soils and structures during various construction stages and post-construction has
been investigated using a “plain strain” deformation analysis mode, based on unfactored“undrained” and “drained” soil parameters.
The Plaxis analysis also enabled to calculate wall deflections and structural forces of individual
members from the Tubular King Pile Foundation system separately, i.e. steel tubular piles and RC
upper wall.

13

5-4-2

Partial Factors

The design uses safety factors obtained from BS EN 1997-1, summarised in Table 5. These factors
are applied to both the actions as well as the material properties.
Combination 1

Combination 2

Set

Set

Design Approach 1
A1

R1

A2

Unfavourable

γG

1.35

1

Favourable

γG;fav

1

1

Unfavourable

γQ

1.5

1.3

Favourable

γQ;fav00Permanent
Actions
Variable

Material
Properties

M1

M2

R1

Reference in
BS EN
1997-1:2004

Table A.3

Angle of shearing
resistance
Effective cohesion

γ φ'

1

1.25

γc'

1

1.25

Undrained shear strength

γcu

1

1.4

Unconfined strength

γqu

1

1.4

Weight density

γγ

1

1

Table A.4

Table 5. Summary of partial factors used for design of retaining walls (after BS EN 1997-1)

The partial factor on variable unfavourable actions in DA1 Combinations 1 is 1.5. However,adopting this approach generates unrealistic and onerous load effects in the piles. According toretaining wall design detailed in Bond & Harris [2008] (Section 12.5.1 page 420), variable actions
should be factored by 1.1 in the analysis (derived from 1.5 divided by 1.35) to give realistic load
effects and then a factor of 1.35 should be applied to the induced load effects in order to obtain
design values. As the factor on the load effects is also applied to effects derived from thepermanent surcharge, it is necessary to reduce the factor on permanent actions to 1.0(1.35/1.35).This approach has been adopted here and is consistent with the guidance in theEurocodes where factors may be applied to actions or effects.

14

5-5

Design Assumptions

5-5-1

Pile Installation Technique

Tubular piles are to be installed by the Gyropress Method that utilises rotary jack-in system with
cutting bits attached on pile toe. It is assumed that ground disturbance is limited to the wall-soil
interface and the properties of soil around the tubular piles are unchanged.
5-5-2

Formation Level

The formation level is at 0.0m AOD, i.e. 7.0m below the top of the RC upper wall / ground surface
level.
The depth of unplanned excavation for ULS calculations has been taken as 0.5m as recommended
by BS EN 1997-1.
5-5-3

Surcharge Load

The geotechnical design of the retaining wall included surcharge loads of 5 kN/m² within 2m fromthe centre line of the upper wall and 20 kN/m² on the verge and carriageway, i.e. outside the
2m-wide area from the upper wall, based on Appendix A of BD 37/01 (Design Manual for Roads
and Bridges).
5-5-4

Impact Load

A single horizontal impact force of 500 kN has been assumed to apply uniformly over a length of
3m along the line of parapet, based on BS 6779-1 and Appendix A of BD 37/01. The mean impact
force at the top of the RC upper wall has been calculated to be 167 kN/m-run.
5-5-5

Serviceability

The allowable horizontal deflection of the cantilevered retaining walls has been aimed at 1% of theretained height, i.e. 70mm.
It should be noted that installation tolerances of the plan position and vertically of the steel sheet
piles need to be added to the calculated deflection in accordance to BS EN 12063 (see Table 6).

15Verticality2) measured
over the top 1m
Type of wall

Situation during execution

Plan position of pile top (mm)%All directions

4)

Sheet pile

On land over water

Primary elementof combined wall

≤

1)

3)

75

≤1

≤ 1001)≤ 1.53)

Depending on soil conditions and on length, shape, size andnumber of secondary elements, these values should beestablished in each case in order to ensure that de-clutching is not
likely occur

1) Perpendicular to the wall.
2) Where the design requires piles to be driven at an inclination, the tolerances specified in the table are withrespect to that direction.
3) May amount to 2% in difficult soils, provided that no strict criteria regarding for example water tightness are
specified and de-clutching is not considered to become a problem after excavation.
4) Excluding straight web piles.
NOTE : The tolerances regarding the position and the verticality may be additive.
Table 6. Tolerances of plan position and vertically of the steel sheet piles after installation(after BS EN 12063)

5-5-6

Pile Section Properties

The pile section properties comprise the elastic modulus of steel or concrete, E, and the pile's
second moment of area, I (moment of inertia), of the section.
1) Steel tubular pile
From the pile properties table, provided in Chapter 3, the moment of inertia for the steel tubularpiles of 1000mm external diameter with the wall thickness of 14mm at 2.5m centres, Istp is 210,846
cm⁴/m.
The steel grade and elastic modulus of the steel piles have been assigned to be S 390 GP and 210
GPa, respectively.
2) RC upper wall
The moment of inertia of the RC upper wall, Iuw, has been calculated as follows:
Iuw = d b³ / 12 / d = 1.0 (1.167)³ / 12 / 1.0 = 13.244 x 10⁶ [cm⁴/m]
where, b : breadth (in-plane) of upper walld : unit width (out-of-plane) of upper wall
The concrete grade has been assigned to be mix strength of C35/45 N/mm². The elastic moduli of
the concrete have been assumed to be 35 and 17.5 GPa for short-term and long-term, respectively.

16

5-5-7

Wall Friction Angle and Adhesion Factor

Based on BS EN 1997-1, the wall friction angle "δ" and adhesion factor "α" between the soil andthe wall has been assumed as presented in Table 7.
Wall friction angle, δWall adhesion factor, αSteel tubular piles

RC upper wall

Granular soil

⅔ φ'peak⅔ φ'peakN/A

Cohesive soil

½ φ'peak½ φ'peakignoredTable 7. Wall friction and adhesion factors used for the retaining wall analysis (after BS EN 1997-1)

5-5-8

Design Life and Durability

The design is required to take into account all foreseeable events that would adversely affect thestability of the retaining structure. Based on Corrosion Rates in Soil, with or without groundwater,a corrosion rate of 1.2mm over the design life of one hundred years has been adopted for the steel
piles in undisturbed natural soils. A check on durability of the steel piles with reduced thickness
has been undertaken.

17

5-6

Assumed Construction Sequence

Sequencing of construction activities will be crucial to ensure that failures do not occur during
construction. Careful consideration will also need to be given to measures required to achieve
ground movement control behind the retaining walls. The following sequence is envisaged for thedesign option and has been used in analyses.
1)
2)
3)
4)
5)
6)

Install steel tubular piles to existing ground level.
Expose pile heads and lay blinding concrete.
Construct RC upper wall using formwork or precast.
Place backfill at the back of the upper wall and compact.
Apply surcharge loads on the active side of the wall to represent surfacing and live load.
Apply water pressure (worst credible case for ULS or moderately conservative case for
SLS).
7) Reduce ground level on the passive side by 0.5m to represent unplanned excavation for
ULS case only.
8) Change geotechnical properties of cohesive soil from "undrained" to "drained"
conditions to represent the long-term soil conditions.
9) Change elastic modulus of concrete from short-term value to long-term value torepresent the effect of creep.
10) Apply an impact load to the top of RC upper wall.

18

5-7

Results

5-7-1

Tubular King Pile Foundation

1) Summary of Results
Results of WALLAP runs and design summary of retaining wall calculations for the Tubular King Pile
Foundation with the toe level of the steel tubular piles at -14.0m AOD are provided in Appendix A.
The bending moments and shear forces obtained from the WALLAP analyses without or with theimpact load are summarised in Table 8 and 9.

Analysis case
(EC7)

Wall
stability

Calculated max.
bending moment

Calculated max.
shear force

Loadfactor(EC7)

Designbending
momentDesignshear
force

Max. wall
top
movement[kNm/m][kN/m]

[mm]

[FoS]

[kNm/m]Elev.
[mAOD][kN/m]Elev.
[mAOD]

1.55

456

-2.40

110

-8.40

1.35

616

149

65

ULS - Comb.1

-

591

-3.60

212

-1.45

1.35

798

286

-

ULS - Comb.2

1.06

1142

-6.10

211

-1.45

1.00

1142

211

-

Designbending
momentDesignshear
force

Max. wall
top
movement[kNm/m][kN/m][mm]

SLS

Table 8. Summary of results from WALLAP analysis without impact load

Analysis case
(EC7)

Wall
stability

Calculated max.
bending moment

Calculated max.
shear force

Loadfactor
(EC7)

[FoS]

[kNm/m]Elev.
[mAOD][kN/m]Elev.
[mAOD]

1.27

1989

-3.60

400

-6.10

1.35

2685

540

345

ULS - Comb.1

-

2590

-4.30

434

-9.60

1.35

3497

586

-

ULS - Comb.2

0.83

4296

-8.40

414

-1.45

1.00

4296

414

-

SLS

Table 9. Summary of results from WALLAP analysis with impact load2) Wall Stability
BS EN 1997-1 requires embedded walls to be designed with sufficient embedment length thatsatisfies vertical, horizontal and moment equilibrium, i.e. a factor of safety above unity is sufficient.
Based on the Design Approach 1 - ULS Combination 2 analysis, using factored surcharge loading,factored soil properties and an additional overdig allowance, the stability of the Tubular King Pile
Foundation has been determined as a minimum factor of safety = 1.06 and 0.83 for the cases
without and with impact load, respectively, as presented in Tables 8 and 9.
Sensitivity analyses indicated that the pile toe level needs to be at least 5m deeper to maintain the
global stability of the foundation under the impact load.
3) Structural Forces (WALLAP)
The wall’s cross section must be verified against structural failure. Based on the Design Approach 1- ULS Combination 1 analysis (WALLAP), using unfactored soil strength, factored surcharge loadings
and an additional overdig allowance, the design bending moment and shear force have been
determined as 798 kNm/m and 286 kN/m, respectively, for the case without the impact load aspresented in Table 8. Under the impact load these design bending moment and shear force
19increased to 3497 kNm/m and 586 kN/m, respectively.
From the wall properties table provided in Chapter 3, the value of the section modulus for the
steel tubular pile "D1000-14 @ 2500" is given as Sstp = 4217 [cm³/m].
The minimum required section modulus for the tubular piles can be calculated as follows:

without impact load
Sreq = Md / fy
= 798·10³ / 390 = 2046 [cm³/m]
where, Sreq : the minimum required section modulus
Md : design bending moment
fy : yield stress of the steel pile = 390 N/mm²→ Degree of utilisation = 2046 / 4217 = 48.5% (OK!)

with impact load
Sreq = Md / fy
= 3497·10³ / 390 = 8967 [cm³/m]→ Degree of utilisation = 8967 / 4217 = 212.6% (to be revised!)

The results indicate that the tubular pile section studied would fail in bending under the impact
load.
4) Structural Forces (PLAXIS)
The Plaxis analysis allows to calculate structural forces of individual members from the Tubular
King Pile Foundation separately, i.e. steel tubular piles and RC upper wall, based on unfactored soil
strength and action.
It should be noted that the effect of the impact load on the retaining structure has not beenmodelled in 2D FE analysis since the type of load is transient.
Output plots from the Plaxis 2D FE analysis without the impact load are provided in Appendix B assummarised in Table 10.

Figure ref.

Plaxis Output Plots

Figure B.1
Figure B.2
Figure B.3
Figure B.4
Figure B.5
Figure B.6
Figure B.7
Figure B.8
Figure B.9
Figure B.10
Figure B.11
Figure B.12
Figure B.13
Figure B.14

Connectivity plot
Total vertical displacements (Short-term)
Total vertical displacements (Long-term)
Total horizontal displacements (Short-term)
Total horizontal displacements (Long-term)
Profile of ground surface settlement behind the wall (Short-term)
Profile of ground surface settlement behind the wall (Long-term)
Deformed mesh |u| (Long-term)
Vector of total displacements (Long-term)
Total shear strain, γs (Long-term)
Distribution of plastic points (Long-term)
Profile of horizontal wall displacements (Long-term)
Profile of wall bending moment for CHS D1000-14 (Long-term)
Profile of wall bending moment for RC upper wall (Long-term)
20

Figure B.15
Figure B.16

Profile of wall shear force for CHS D1000-14 (Long-term)
Profile of wall shear force for RC upper wall (Long-term)

Table 10. Summary of output plots from Plaxis 2D FE analysis for Tubular King Pile Foundation

By comparing the profiles of structural forces for the steel tubular pile (Figures B.13 and B.15) and
the RC upper wall (Figures B.14 and B.16), it can be seen that the steel tubular pile is carrying thelarger magnitude of bending moment while similar magnitude of shear force is calculated for both
members.
The maximum bending moment (431 kNm/m) is recorded at the upper portion of the steel tubularpiles (at -2.50m AOD) and reduced to 231 kNm/m at the base of the RC upper wall before
becoming zero at top of the upper wall.
Both the bending moment (BM) and the shear force (SF) calculated by Plaxis are comparable tothose calculated by WALLAP SLS analysis (i.e. BM = 456 kNm/m and SF = 110 kN/m).
5) RC Upper Wall
Based on the Design Approach 1 - ULS Combination 1 analysis (WALLAP), the design bending
moment and shear force have been calculated as 341 kNm/m and 140 kN/m, respectively.
The reinforcement steel to resist bending moments and shear forces induced in the upper wall has
been determined as follows: T32 vertical bars at 150mm centres; and T25 horizontal bars at 150mm centres.
6) Durability
Based on the corrosion rate of 1.2mm over the design life of one hundred years, the reduced
section modulus for the steel tubular pile "D1000-14 @ 2500" can be calculated as follows:
Sred = π (do⁴ - di⁴) / 32 / do / s= π [(1000 - 1.2 x 2)⁴ - (972 + 1.2 x 2)⁴]/ 32 / (1000 - 1.2 x 2) /·10³ / 2.5 = 3502 [cm³/m]
where, Sred : the reduced section modulus due to corrosion
do : external diameter of tubular pile [mm]di : internal diameter of tubular pile [mm]s : tubular pile spacing [m]A check on durability of the steel piles can be undertaken by calculating the degree of utilisation
for the minimum required section modulus, Sreq, against the reduced section modulus, Sred, as
shown below.


Degree of utilisation without impact load
= Sreq / Sred = 2046 / 3502 = 58.4% (OK!)

21

7) Serviceability
The maximum wall top deflection by the WALLAP SLS analysis was calculated as 65mm at thelong-term case without the impact load as presented in Table 8. Conversely, based on the Plaxis 2D
FE analysis under the same loading conditions, the wall movement was calculated to be 80mm asshown in Figure B.12 (Appendix B). The difference in wall movement between these calculations isdue to the effect of consolidation that has explicitly been modelled by Plaxis software.
The predicted ground movements by Plaxis are presented in Figures B.2 to B.9 (Appendix B). The
settlements at immediately back of the upper wall are 70mm and 84mm for short-term andlong-term cases, respectively, reducing almost linearly to 5mm at 15m away from the wall.
Figures B.10 and B.11 show the development of the active wedge from the surface point at 5m
away from the wall down to the formation level.
8) Vehicle Restraint Barrier
As presented above, the Tubular King Pile Foundation system studied is likely to suffer geotechnicaland structural failure when the impact load is applied at the top of the RC upper wall. It is,therefore, recommended to specify an appropriate "Working Width" (i.e. width of the restraint
system + its maximum dynamic lateral deflection + vehicle intrusion beyond the restraint system"overhang" after BS EN 1317-2) between the vehicle restraint barrier and the RC upper wall.
If there is a requirement to install vehicle restraint barrier on or adjacent to the RC upper wall due
to constraint on available land/space and etc., it may be possible to do so by increasing tubular pile
sections and reducing the pile spacing.
9) Pedestrian Protection at Retaining Walls
Pedestrians are not normally expected to be present near retaining walls on motorways. However,drivers and passengers of broken down or damaged vehicles, maintenance staff, emergency
service personnel and others may need to walk near them and there is a potential danger of
persons falling from the top the wall, particularly in poor visibility or adverse weather conditions[after TD 19/06 (Design Manual for Roads and Bridges)]. Hence, it is recommended to erectpedestrian restraint system, e.g. handrail, along the top of the RC upper wall.

22

5-8

Summary

A summary of design of the Tubular King Pile Foundation is presented in Table 11 and Figure 6.

Wall type

Tubular pile

RC wall

Material

Pile section /Wall width

Steel

D1000-14

S 390 GP@ 2500mm c/c

Concrete

Top: 500mm

C 35/45

Base: 1167mm

Pile / WalllengthPile / Wall
top elevation[m][m AOD]

14.0

7.0

7.0

0.0

Reinforcement

T32 vertical bars @ 150 c/c
T25 horizontal bars @ 150 c/c

Table 11. Summary of design of Tubular King Pile Foundation

Figure 6. Section showing design of the Tubular King Pile Foundation

23

APPENDICESAPPENDIX A

Design of Tubular King Pile Foundation based on WALLAP

APPENDIX B

Plaxis 2D FE Analysis of Tubular King Pile Foundation

APPENDIX A
Design of Tubular King Pile Foundation based on WALLAP
A-1. WALLAP run ID: TKPF_D1000-14at2500_Toe-14m_Fill+7m_STLT_SLS
A-2. WALLAP run ID: TKPF_D1000-14at2500_Toe-14m_Fill+7m_STLT_ULS1
A-3. WALLAP run ID: TKPF_D1000-14at2500_Toe-14m_Fill+7m_STLT_ULS2

APPENDIX B
Plaxis 2D FE Analysis of Tubular King Pile Foundation
Figure B.1

Connectivity plot

Figure B.2

Total vertical displacements (Short-term)

Figure B.3

Total vertical displacements (Long-term)

Figure B.4

Total horizontal displacements (Short-term)

Figure B.5

Total horizontal displacements (Long-term)

Figure B.6

Profile of ground surface settlement behind the wall (Short-term)

Figure B.7

Profile of ground surface settlement behind the wall (Long-term)

Figure B.8

Deformed mesh |u| (Long-term)

Figure B.9

Vector of total displacements (Long-term)

Figure B.10

Total shear strain, γsFigure B.11

Distribution of plastic points (Long-term)

Figure B.12

Profile of horizontal wall displacements (Long-term)

Figure B.13

Profile of wall bending moment for CHS D1000-14 (Long-term)

Figure B.14

Profile of wall bending moment for RC upper wall (Long-term)

Figure B.15

Profile of wall shear force for CHS D1000-14 (Long-term)

Figure B.16

Profile of wall shear force for RC upper wall (Long-term)(Long-term)

24

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